Recently, in manufacturing semiconductor devices, semiconductor wafers (hereinafter, referred to as “wafers”) as substrates to be processed undergo an intended process one by one while being mounted on a wafer mounting table. In this case, it is important to ensure reproducibility when a plurality of wafers is processed, and to uniformly process the surface of a single wafer sheet. For example, when a plasma etching process is performed on a wafer, it is preferable that the substrate mounting table have a temperature control function for controlling the temperature distribution in the surface of the wafer to allow, e.g., a chemical reaction to be uniformly carried out, thereby uniformly processing the surface of the wafer.
As a conventional approach dealing with the temperature control function of the substrate mounting table, there has been proposed in, e.g., Japanese Patent Laid-open Publication No. 9-17770 (e.g., the abstract) a plasma processing method wherein two coolant passageways, that is, an inner and an outer coolant passageway, are provided in the substrate mounting table so that there occurs a temperature difference between the two passageways to offset a non-uniform temperature distribution on the wafer. Therefore, a uniform temperature in the surface of the wafer is achieved.
Generally, a substrate mounting table for mounting thereon a wafer uses a metal material having an excellent thermal conductivity, such as aluminum. Thus, even though two coolant passageways are provided to cause the temperature difference in the substrate mounting table as in the above-mentioned conventional method, there may occur heat transfer therein. Accordingly, temperature controllability thereof is poor, and it is difficult to provide a desired temperature difference. In other words, even if two coolant passageways are provided, the boundary between the two passageways is not definite, so that it is difficult to rapidly control temperature due to the heat transfer therebetween, thereby making it impossible to precisely control the temperature distribution of the substrate mounting table. As a result, it is problematic in that the temperature is not made sufficiently uniform in the surface of the wafer, and consequently, a process is not conducted sufficiently uniformly.